Photographic light-sensitive materials often have colored emulsion layers and other hydrophilic colloidal layers colored in order to absorb light within specific wavelengths. When necessary to control the spectroscopic composition of light falling on a light-sensitive layer, a colored filter layer further removed from the base than the emulsion layer is usually employed. In films containing multiple emulsion layers, a filter layer is sometimes positioned between the emulsion layers.
Colored filter layers usually incorporate water-soluble dyes to provide the necessary color. Such dyes must have the right spectral absorption for the intended purpose and be photochemically inert; that is, they must have no chemically adverse effect on the performance of the photographic quality of the film such as reduction of sensitivity, degradation of latent image, fogging, and the like. In this context, the dye used should not exert a spectral sensitizing effect on an emulsion which should not be spectrally sensitized. Nor should they lower the degree of spectral sensitization of an emulsion which has been spectrally sensitized or broaden, narrow, or shift wavelength or create a new maximum wavelength for spectral sensitization.
Dyes used in a filter layer should discolor or be eluted into the treating solution or wash water during development in order not to leave detrimental color on the light-sensitive material being treated. While a number of methods are available for selectively coloring a colloidal filter layer, often a hydrophilic polymer having an electric charge opposite that of the dye ions is added to the hydrophilic colloidal layer as a mordant which interacts with the dye molecules to contain the dye locally in a specific colloidal layer. When mordanting with a polymer is used, the contact of the dye containing layer with the other colloidal layers in a wet condition often results in diffusion of the dye from the former into the latter layer. This diffusion depends on the chemical structure of the mordant used and the structure of the dye involved.
When a high molecular weight mordant is used, color is likely to remain on the light-sensitive material after photographic treatment, particularly when shortened processing times are used. Presumably, this is caused by retention of dye or a product of reversible discoloration in the layer containing the mordant. The mordant can recombine with the dye even in a developing solution, depending on the structure of the mordant and nature of the dye employed.
Various dyes have been proposed as offering possible solutions to such problems. U.S. Pat. Nos. 3,672,898; 4,345,017; 4,059,448; and 4,268,622 describe indolenes, butadienes, styryls, pyrazolones, cyanines, and the like as possible candidates. Japanese Kokai Patent Nos. 50-28827, 58-21247, and 58-4142 describe dispersions of dyes in alkali soluble resins. Such dyes nevertheless tend to spectrally sensitize a photographic emulsion which has not been spectrally sensitized and alter the degree of spectral sensitization of an emulsion which has been spectrally sensitized. Great Britain Patent 545,529 describes azo dyes having a resinous nature and 506,385 describes oxonol dyes irreversibly decolored in developers containing sulfite which do not adversely influence the photographic properties of photographic emulsions. However, such dyes cannot be mordanted adequately and diffuse from the basic polymer containing layer to other layers. Further, strong mordanting to control dye mobility leads to inhibition of sulfite bleaching.
The need for nonwandering filter dyes, particularly for blue and green X-ray film, is critical to reduce crossover exposure and reduce sensitizing dye stain, particularly in green X-ray film. In photosensitive film, nonwandering filter dyes prevent blue light punch through onto green sensitive emulsions and, particularly in microfilm, are needed to eliminate hypo retention and filter dye stain which results from the use of mordants currently employed.